1. Technical Field of the Invention
The present invention relates to an image recording device that compresses and records the digitalized image signals.
2. Description of the Related Art
The digital value of the compressed data of the prior image recording device is normally restricted, which device digitalizes images and subjects the same images to compression coding for recording. For instance, as for a DVD-RAM recorder, the bit rate thereof is defined according to the recording speed, volume and the maximum recording time of the medium in use, which requires the digital value of the compressed images data to be restricted to a given value or below. Thus, when the digital value of the images data prior to compression is large such as high-precise and complicated images and the same value of the compressed images data goes beyond the definitive bit rate, it is controlled such that the compressibility of the subject data is enhanced so as to reduce the digital value of the compressed images data. However, the enhancement of such compressibility occurs block and mosquito noises and as such, which damages the quality of the images.
As an example of the prior art to restrain such noises caused by such high compression of the images data as mentioned above, it is disclosed in Japanese Patent Laid-open No. H9-172637 that when the compressibility of the images is high, the passing band of the images signals prior to compression is narrowed through a band restriction filter so as to belittle the digital value of the images signals prior to compression, which allows the compressibility thereof to be rendered lower so as to restrain the block and mosquito noises and as such.
In the above disclosure, the narrowing of the passing band of the low-pass filter leads to the lowering of the resolution of the images, in which there is likelihood to deteriorate the recorded signals prior to compression when the compressibility of the data is high.
The enhanced compressibility of the data and the increased digital value of the compressed data are caused by the complexity of the images themselves and another factors, one of which is a frame noise. The frame noise is not inherent in the images, but it increases the digital value of the images data in the same way as the complexity thereof. Further, the other factor is a lower correlation between frames. For example, in such compression technique as represented by MPEG2, in principles, the lower correlation between frames incapacitates the highly efficient compression of the data, which results in enlarging the compressibility thereof or increasing the digital value of the compressed images data. In the above prior reference, there is no disclosure to reduce the compressibility thereof or the digital value of the compressed data against the issues wherein the influence of the frame noises is enormous so as to worsen the S/N ratio and the correlation between the frames is low.
In view of the above unsolved prior issues, it is an object of the invention is to provide an image recording device that records the images with such frame noises as block and mosquito noises in restraint by lowering the compressibility of the digitalized signals or improving the compression efficiency thereof without deteriorating the signals prior to compression so as to reduce the digital value of the compressed images data.